Tractate Berakhot of the Talmud of Eretz-Israel: 0006

1:
So far we have established that the halakhic day may be divided into several periods of unequal length. There is daytime, there is nighttime, and there is twilight, which separates them. Daytime ends with the setting of the sun. But how long is this period that we call twilight? How long does twilight last?

2:
Among the sages there are two opinions. One opinion is that it is not possible to tell when twilight begins and ends. The other opinion is that it is possible to define the period called twilight. The Gemara first quotes the opinion of Rabbi Tanḥuma, that twilight lasts as long as it takes a drop of blood on the tip of a spear to begin to drip down the sides of the spear: in other words, twilight lasts no time at all.

3:
However, the Gemara now brings another barayta, which presents two views: that of Rabbi Neḥemyah and that of Rabbi Yosé. Rabbi Neḥemyah defines the extent of twilight as being similar to the time it takes a man to walk half a mil. The unit of measurement mil represents the Roman mile, which can be defined as one thousand paces at the regular marching length of the Roman army. Each pace was two steps so the resultant mile was approximately 1500 metres. In Eretz-Israel this distance was adapted to fit in with other local systems of measurement, so the mil was defined as 2000 cubits. This yields a mil of approximately 1.12 kilometres. So, according to Rabbi Neḥemyah, from the moment that the top of the sun's disc dips below the horizon one can estimate the time it would take to walk 500 or so metres (presumably at the regular Roman military pace) and that would give an indication of the end of twilight and the onset of night.

4:
As we noted, the barayta also quotes the differing view of Rabbi Yosé. (This refers to Rabbi Yosé ben-Ḥalafta, a colleague of Rabbi Neḥemyah.) He holds that twilight is as long as the blink of an eye. In other words, it is not possible to define when twilight begins and ends; it is too sudden.

5:
The Gemara now attempts to reconcile these two views as to the length of twilight. We are told that two sages, Rabbi Yosé and Rabbi Aḥa, were engaged in study. (This is a different Rabbi Yosé: this is Rabbi Yosé the amora, who lived at the end of the 4th century and the beginning of the 5th. We gave a short biography of him in 0001.) Rabbi Aḥa stated what seems obvious: the two views cannot be reconciled. Either twilight is virtually instantaneous (as held by Rabbis Tanḥuma and Yosé) or it lasts for several minutes (as held by Rabbi Neḥemyah). His study partner, Rabbi Yosé agreed with him. However, a third sage, Rabbi Ḥizkiyah, held that the two views can be reconciled.

6:
Rabbi Ḥizkiyah holds that the definition of Rabbi Neḥemyah is essentially correct and that Rabbi Yosé ben-Ḥalafta does not disagree with his assessment. What Rabbi Yosé wanted to say was that the whole of that period defined by Rabbi Neḥemyah is definitely twilight. Each second — each blink of an eye — is completely twilight; there are no 'rough edges'.

7:
The commentary Pney Moshe (see 0002.) gives a fuller explanation:

Let us put this as simply as possible. Rabbi Yosé holds that it is either day or it is night; there is no 'in between'. Our mishnah says that the time for reading Shema at night time is around the time when priests go to the mikvah. That time, according to Rabbi Yosé, extends right up to the end of twilight according to Rabbi Neḥemyah. (Rabbi Neḥemyah would, presumably, hold that a priest must bathe before his twilight begins because for him day time ends with the onset of twilight.)

This part of the discussion is not yet concluded!